1、Designation: D 6747 04Standard Guide forSelection of Techniques for Electrical Detection of PotentialLeak Paths in Geomembranes1This standard is issued under the fixed designation D 6747; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard guide is intended to assist individuals orgroups in assessing different options availa
3、ble for locatingpotential leak paths in installed geomembranes through the useof electrical methods. For clarity, this document uses the termpotential leak path to mean holes, punctures, tears, knife cuts,seam defects, cracks and similar breaches over the partial orentire area of an installed geomem
4、brane.1.2 This guide does not cover systems that are restricted toseam testing only, nor does it cover systems that may detectleaks non-electrically. It does not cover systems that onlydetect the presence, but not the location of leaks.1.3 This standard does not purport to address all of thesafety c
5、oncerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory requirements prior to use.2. Referenced Documents2.1 ASTM Standards:2D 4439 Terminology for Geosynthetic
6、s3. Terminology3.1 Definitions:3.1.1 electrical leak location, nany method which useselectrical current or electrical potential to detect and locatepotential leak paths.3.1.2 geomembrane, nan essentially impermeable mem-brane used with foundation, soil, rock, earth or any othergeotechnical engineeri
7、ng related material as an integral part ofa manmade project, structure, or system.3.1.3 geosynthetic, na planar product manufactured frompolymeric material used with soil, rock, earth, or other geo-technical engineering related material as an integral part of amanmade project, structure, or system.3
8、.1.4 potential leak paths, nfor the purposes of thisdocument, a potential leak path is any unintended opening,perforation, breach, slit, tear, puncture, crack, or seam breach.Scratches, gouges, dents, or other aberrations that do notcompletely penetrate the geomembrane are not considered.Leak paths
9、detected during surveys have been grouped into fivecategories: (1) Holesround shaped voids with downward orupward protruding rims, (2) Tearslinear or areal voids withirregular edge borders, (3) Linear cutslinear voids with neatclose edges, (4) Seam defectsarea of partial or total separa-tion between
10、 sheets, and (5) Burned through zonesareaswhere the polymer has been melted during the weldingprocess.4. Significance and Use4.1 Types of potential leak paths have been related to thequality of the sub-grade material, quality of the cover material,care in the cover material installation and quality
11、of geomem-brane installation.4.2 Experience demonstrates that geomembranes can haveleaks caused during their installation and placement of mate-rial(s) on the liner.4.3 The damage to a geomembrane can be detected usingelectrical leak location systems. Such systems have been usedsuccessfully to locat
12、e leak paths in electrically-insulatinggeomembranes such as polyethylene, polypropylene, polyvinylchloride, chlorosulfonated polyethylene and bituminousgeomembranes installed in basins, ponds, tanks, ore and wastepads, and landfill cells.4.4 The principle behind these techniques is to place avoltage
13、 across a synthetic geomembrane liner and then locateareas where electrical current flows through discontinuities inthe liner (as shown schematically in Fig. 1). Insulation must besecured prior to a survey to prevent pipe penetrations, flangebolts, steel drains, and batten strips on concrete to cond
14、uctelectricity through the liner and mask potential leak paths. Theliner must act as an insulator across which an electricalpotential is applied. This electric detection method of locatingpotential leak paths in a geomembrane can be performed on1This guide is under the jurisdiction ofASTM Committee
15、D35 on Geosyntheticsand is the direct responsibility of Subcommittee D35.10 on Geomembranes.Current edition approved Nov. 1, 2004. Published November 2004. Originallyapproved in 2002. Last previous edition approved in 2002 as D 674702e12For referenced ASTM standards, visit the ASTM website, www.astm
16、.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.FIG. 1 Sch
17、ematic of Electrical Leak Detection MethodD6747042exposed liners, on liners covered with water, or on linerscovered by a protective soil layer, or both.5. Developed Systems5.1 Electrical leak detection systems were developed in theearly 1980s and commercial surveys have been available since1985. A s
18、hort description of these systems is presented in thissection.5.2 The Water Puddle and Water Lance SystemThe tech-nique is appropriate to survey a dry uncovered geomembraneduring its installation when placed directly on a subgrade thatis an electrically conductive layer below the geomembrane.The low
19、er conductive layer is usually the soil and the upperconductive layer being water. A cathode ground is establishedand an anode is placed in a water puddle maintained by asqueegee or to the water stream of a lance (as shownschematically in Fig. 2). Water is usually supplied by gravityfrom a tank truc
20、k parked at a higher elevation than the linedarea. For this technique to be effective, the leaking water mustcome into contact with the electrical conducting medium towhich the ground electrode of the 12 or 24 volts dc supply canbe connected. Since the geomembrane is not a perfect electricalinsulato
21、r, a steady background signal can be audible. As thewater flows through a leak path, there is an increase in thesignal. Leak paths as small as 1 mm in size are then located byan audio signal or by measuring a current of magnitude relatedto the size of the leak. It can also be used to search for leak
22、paths in geomembrane-lined concrete and steel tanks.5.2.1 FeaturesThe main advantage of this system is thepossibility to detect leak paths in geomembrane joints andsheets as work progresses during the construction phase.Larger leak paths do not mask smaller ones because thistechnique locates leak pa
23、ths independently on uncovered liner.The electrical survey rate of approximately 500 m2/h peroperator does not affect the installation work schedule andpermits a rapid construction quality control (CQC) of theinstaller work. The approximate setup time varies from 1 to 3h.5.2.2 LimitationsThis techni
24、que cannot be used with aprotective layer covering the liner. The presence of wrinklesand waves, steep slopes and lack of contact between the linerand the conductive soil at bottom of slopes inhibits the surveyspeed. This technique cannot be used during stormy weatherwhen the membrane is installed o
25、n a desiccated subgrade, orwhenever conductive structures cannot be insulated or isolated.The procedure to detect potential leak paths in seams of repairpatches is difficult and lengthy since it requires a certaininfiltration time.5.3 The Water-Covered Geomembrane SystemThe prin-ciple behind this sy
26、stem is to test the geomembrane while it iscovered with water, a technique similar to the previous systemrequiring an electrically conductive layer below (subgrade) andabove the liner (water or saturated drainage layer). A cathodeground is established and an anode is placed in containedwater. The vo
27、ltage impressed across the liner (by a high voltagedc or ac power supply) produces a low current flow and arelative uniform voltage distribution in the material above thegeomembrane. To maximize this current, a high voltage powersupply with safety circuits is used that can provide up to 400volts DC.
28、 A hand-held probe is then traversed through thewater. An electrical current flows through the potential leakpaths causing localized abnormalties in the electrical paths asshown schematically in Fig. 3. The typical procedure is to floodthe test area, then locate the potential leak paths, drain the a
29、reaand perform repairs. A hand-held probe or a probe on a longcable is scanned through the water to locate these places wherecurrent is flowing through a leak. A typical procedure is toflood the test area to a depth of approximately 0.15 to 0.75 m.This technique can locate very small leaks, smaller
30、than 1 mm.The signal amplitude is proportional to the amount of electricalcurrent flowing through the leak, so practical measures shouldbe taken to maximize the current through the leaks. The signalamplitude is inversely related to the distance from the leak, sothe scanning spatial frequency should
31、be designed to providethe desired leak detection sensitivity.5.3.1 FeaturesThis system has the advantage of beingused to locate potential leak paths in in-service impoundments.Primary and secondary liners can be tested. The water head onthe liner facilitates the survey speed by minimizing thepresenc
32、e of wrinkles and waves, and lack of contact betweenthe liner and the conductive soil at the bottom of slopes. Thistechnique can be used in wet conditions. The main advantageof this technique is the detection of leak paths with theprotective granular layer covering the liner (after the installa-tion
33、 of the drainage layer on the geomembrane) (refer to 5.5 fordescription of the method). The survey rate depends primarilyon the spacing between sweeps and the depth of the water. Aclose spacing between sweeps is needed to detect the smallestleaks. The survey rate for a survey while wading, sweeping
34、theprobe so that it comes within 0.25 m of every point on thesubmerged geomembrane is 800 to 1200 m2/h per person. Fora survey with a towed probe with the probe scanned within 0.4m of every point, the survey rate is 800 to 1000 m2/h per twopersons, including establishing the survey lines. The approx
35、i-mate setup time is 30 to 90 min. These times do not include thetime to flood the liner.5.3.2 LimitationsThe main disadvantage of this system isthat it cannot be applied to detect potential leak paths ingeomembrane joints and sheets as work progresses during theconstruction phase since, because of
36、the need to flood thegeomembrane with water. The presence of large leak paths mayinfluence the detection of small leak paths in their vicinity.Depending on the bottom configuration of the surveyed appli-cation, the water depth can be substantial in some areas; theprocedure is more lengthy consisting
37、 of flooding the area,probing to locate the leak paths and draining of the area toperform repairs.5.4 The Electrically Conductive GeomembraneCoextrusion technology makes possible the manufacture of apolyethylene geomembrane that can be spark tested. Thematerial has a thin layer of electrically condu
38、ctive material asan integral part of the geomembrane. This provides a way tospark test the installed geomembrane. The spark testing thatoccurs in the field is very similar to the method used in thefactory to identify holes during geomembrane manufacturing.The conductive geomembrane is installed such
39、 that the con-ductive side is against the sub-base and the non-conductiveD6747043side is on top. The testing utilizes a voltage source to charge anelement such as an electrically conductive neoprene pad. Thecharge is then transferred to the (underlying) conductive layerof the geomembrane through the
40、 capacitance effect. Anotherconductive element is then swept over the upper surface toinspect for the presence of potential leak paths. Where apotential leak path occurs, a closed circuit is created and aspark is produced as shown in Fig. 4. To facilitate leak pathFIG. 2 Schematic of Water Puddle an
41、d Lance SystemsD6747044location, equipment must include an audible alarm. Different types of equipment are utilized depending on the area to beFIG. 3 Schematic of Water-Covered Geomembrane SystemD6747045tested. For example, small, hand-held detectors are used inconfined areas and large detectors can
42、 be used on large, openareas.5.4.1 FeaturesThe main advantages of this technique are:this is the only system that utilizes a conductive groundinglayer that is an integral part of the membrane being tested thuseliminating the issue of inconsistent grounding; it can beperformed during construction; no
43、 water pumping is required;current flow is miniscule; primary and secondary liners can betested; all slopes can be tested; it can detect leak paths smallerthan 1 mm. The rate of testing depends on the type ofequipment used. Using a 2-m wide brush, travelling at 3 to 5km/h, the rate can be up to 5001
44、,500 m2/h. Repairs can beperformed immediately upon location of a leak path. The setuptime required is approximately 30 min.5.4.2 LimitationsThe presence of wrinkles and waves andsteep slopes inhibits the survey speed. This technique cannotbe used during stormy weather. The location of leak paths wi
45、ththe protective granular layer covering the liner is not possible.It is not the intention of this method to replace traditionalnon-destructive testing of seams since a conductive paththrough the conductive layer on the bottom of the upper flap ofa fusion weld seam must be conducted with a lower vol
46、tageand lower leak detection sensitivity.5.5 The Soil-Covered Geomembrane SystemThis methodtests the geomembrane after the protective soil layer is em-placed. As shown in Fig. 5, it is similar to the water-coveredgeomembrane method except the geomembrane is coveredwith soil during the survey, and po
47、int-by-point measurementsare made on the surface of the soil. The soil must have somemoisture, but it does not have to be saturated with water. Itrequires an electrically conductive layer below the geomem-brane. The most common implementation of this method is tomake dipole measurements using two mo
48、ving electrodesspaced a constant distance apart. Pole measurements can alsobe made by making potential measurements on the protectivesoil cover using one moving electrode referenced to a seconddistant electrode. The data can be taken on a grid or at regularpoints along parallel survey lines. The dat
49、a can be plotted in thefield and analyzed to locate areas with a characteristic leaksignal. The data can be analyzed in raster data form or usingcontour plots.5.5.1 FeaturesThis method has the distinct advantage oflocating potential leak paths that are made during the emplace-ment of the protective soil layer. These construction damageleaks have been found to be prevalent type of damage togeomembranes that are difficult to detect during constructionactivities. This technique can be used in wet conditions. Withproper signal sampling, this technique can locate sm
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